1. Field of the Invention
The present invention relates to optical communication systems, and more particularly to the optical receiver of an optical cross-connect device.
2. Description of the Related Art
In an optical communication system, an optical cross-connect device is typically installed at an intermediate node connecting together the upper node, such as a central base station, and the lower node, such as a subscriber. In addition to the basic functions of transferring and allocating channel signals, the optical cross-connect device plays viable functions of optimizing the data traffic in an optical network and the growth of the network, while improving the abnormal congestion and survivability of the network. In particular, an optical cross-connect device is used in a wavelength division multiplexing (WDM) system and typically includes a demultiplexer, an optical receiver, a cross-connect switch, a controller, an optical transmitter, and a multiplexer.
A conventional receiver in a multi-channel optical communication system typically operates at a particular predetermined bit rate. Hence, the receiver is bit-rate specific. There are diverse transfer formats, known as “protocols,” that are available in optical communication systems. For example, representative transfer formats include SDH/SONET (Synchronous Digital Hierarchy/Synchronous Optical NETwork), FDDI (Fiber Distributed Data Interface), ESCON (Enterprise Systems CONnectivity), optical fiber channel, gigabit Ethernet, and ATM (Asynchronous Transfer Mode). These different protocols provide diverse bit rates of 125 Mb/s, 155 Mb/s, 200 Mb/s, 622 Mb/s, 1,062 Mb/s, 1.25 Gb/s, and 2.5 Gb/s, respectively.
As mentioned above, optical signals may be inputted to the optical receiver of an optical cross-connect device at diverse bit rates. To this end, the optical receiver is provided with a self-healing means for the bit rate, such that it has the flexibility to meet diverse is protocols with different bit rates. Various mechanisms are known to process optical signals in a bit-rate independent manner.
FIG. 1 is a block diagram illustrating the configuration of a conventional self-healing apparatus employed in an optical receiver. As shown in FIG. 1, the conventional apparatus includes an optoelectric converting unit 10 for converting an input optical signal into an electrical signal as a receiving signal; an amplifying unit for amplifying the receiving signal outputted from the optoelectric converting unit 10; and, a bit rate discriminating unit 30 for outputting a bit-rate sensing signal generated by exclusively OR'ing the receiving signal with a delay signal generated by delaying the amplified receiving signal by a predetermined time. The self-healing apparatus also includes a clock/data reproducing unit 40 for receiving the signal and reproducing clocks and data based on the reference clock; a bit rate signal generating unit 50 for generating the reference clock in response to a bit rate change signal received therein; and, a control unit 60 for determining the bit rate of the receiving signal based on the voltage level of the bit-rate sensing signal outputted from the bit rate discriminating unit 30 and for outputting the bit rate change signal based on the determined bit rate.
FIG. 2 is a flow chart illustrating a conventional self-healing procedure performed by the control unit. As shown in FIG. 2, the self-healing procedure involves the steps of determining whether there is an optical signal received in the optical receiver based on the formation of an LOS signal outputted from the amplifying unit 20 (Step S10); determining whether there is a change in the bit rate of the received optical signal based on the voltage level of a recognition signal generated in association with the received optical signal (Step S20), and, if it is determined at step S20 that there is a change in the bit rate, then outputting a bit rate change signal corresponding to the changed bit rate to the bit rate signal generating unit 50.
However, the conventional self-healing device, as described above, involves a high probability that errors will occur when determining the bit rate due to a temperature variation in the optical receiver, as there is no compensation means to address the temperature variation. That is, the DC level of the recognition signal is used as a reference for the determination of the bit rate, without providing any compensation associated with the temperature variation.